Summary
This document proposes superseding an existing airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S- 76A, S-76B, and S-76C helicopters. That AD currently requires, before further flight, performing a fluorescent penetrant inspection (FPI) of the main rotor shaft assembly (shaft). Also, a recurring FPI and visual inspection for a cracked shaft are required by that AD. That AD also requires replacing the shaft with an airworthy shaft before further flight if a crack is found. This action would require replacing certain serial numbered shafts with an airworthy shaft before further flight. This proposal is prompted by a further investigation and a determination that the inspections can be safely eliminated if certain serial numbered shafts are removed from service before further flight. The actions specified by the proposed AD are intended to prevent failure of the shaft and subsequent loss of control of the helicopter.